Richard Feynman QED Lecture 2, Reflection and Transmission : 3/7

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Recommends Acccumulation · 2020-03 · Physics Stack Exchange · on “Why do photons follow specific path after reflection from a mirror surface if they can be emitted in any direction by electrons of mirror surface?”

It's the same reason that light follows a straight path in a constant medium and follows Snell's laws when changing medium: there's destructive interference between all the other paths. You can actually get light to reflect at another angle if you remove parts of the mirror. If you do it right, the parts of the wavefunction going in the new direction remain, and the ones interfering with them disappear. Which parts of the mirror need to be removed depend on the frequency of the light (you can also do this with transmission: if you cut slits in a sheet strategically, you can get light going through it to bend by having only the diffraction in the desired direction survive). Here's a Feynman l

Cites Errol Hunt · 2016-11 · Physics Stack Exchange · on “Feynman's superposition explanation of reflection/refraction, and 'tricking' quantum physics”

In the Auckland Uni lectures [this video] , Professor Feynman explains refraction and reflection from a quantum superposition point of view. Ie, a photon of light can take any possible path, and the chances of seeing it at any measurement point is the superposition of all the various paths that it could have taken to get there. He uses phase arrows quite cleverly to show the effect of summing phase differences with the different path lengths. Eg, that two paths that have the photon arriving precisely 180deg out of phase will cancel out. This shows that most measurement points will see nothing, because for them, the many different paths will all cancel out. But for that particular measurement poin

Cites Capo Mestre · 2024-05 · Physics Stack Exchange · on “Reflection due to wave nature of light”

PERFECT MIRROR One can think of the reflection as constructive/destructive interference of waves (see Figure 1). In order to reach a detector (e.g., human eye), light waves from a point light source can in principle travel all these trajectories shown in Figure 1 (there is always a non-zero probability for that to happen). Then, one just has to sum up all these waves together in the immediate proximity of the detector. Considering only parts of trajectories that have same length from the detector (i.e., between black markers and the detector in Figure 1), the phase of light waves at the detector for trajectories that are away from reddish ones accumulates much faster than the phase of light